1. Field of the Invention
The present invention relates to control of a DC—DC converter, and more particularly to a control circuit and its control method of a DC—DC converter which can be composed easily in a logic circuit.
2. Description of the Related Art
In a control circuit for a DC—DC converter of synchronous rectifying switching type having an analog error amplifier, the analog error amplifier has a resistance or a capacitor as a feedback circuit. In the event of fluctuations of an input voltage of a DC—DC converter, or variable control of an output voltage of a DC—DC converter, the error amplifier is required not to oscillate. In order to set a gain to have an allowance in a phase of the feedback circuit, the phase compensation of the feedback circuit must be designed in consideration of the relation of an input and an output voltage at the time of design of the DC—DC converter. That is, it is necessary to control the gain statically.
Other related technologies are disclosed in Japanese unexamined patent application publication No. 9-154275 and Japanese unexamined patent application publication No. 10-323026.